1. Field
This patent specification relates to a method of recycling two-components electrostatic image developers for use in electrophotography and electrostatic recording, capable of separating carrier coating materials from core materials of a carrier composite which includes at least metal containing magnetic materials and resinous materials, to subsequent recycling as a carrier, through processes benign to the environment and without affecting the properties of the core materials.
2. Discussion of the Background
In electrophotography, developers are used to render a latent image visible. The developed image is then transferred to paper and fixed to create resulting copy. Of these developers, two-component dry developers are known, which contain both toner and carrier.
Minute particles of the toner are held on the surface of the carrier particles of relatively large sizes. In addition to the magnetic force, which acts between the carrier particles themselves and is utilized for carrying toner particles, there are electrostatic and adhesive forces in the two-component development.
The adhesive force between the charged toner and the oppositely charged carrier bead is overcome by the development force produced on the toner by the photoreceptor surface charge distribution of a latent image. As a result, the toner particles are transferred selectively onto the photoreceptor to form the developed electrostatic image. Subsequently, the electrostatic image is fixed as indicated above.
The carrier for use in two-component dry developers of the present disclosure is made of at least magnetic particles and resinous materials. Examples of the carrier structure may also include, among others, layers of resinous materials coated on top of magnetic particles having relatively large sizes, and magnetic particles with a relatively small sizes, dispersed uniformly in the resinous materials.
The carrier particles are not intended to be consumed in use and generally are used repeatedly, with toner particles added to replenish those used up in producing copies. Therefore, it is desirable for the carrier to maintain its capability to impart, through frictional charging, an appropriate polarity and a sufficient amount of charge to toner particles throughout the repeated usage.
Previously known developers, however, tend to change their charging characteristics, due to factors such as collision with either toner particles themselves or walls of the developer housing. This can result in carrier surface changes such as cracks, fracturing and abrasion of carrier coatings, and compression of toner particles, thereby leading to so-called ‘spent’ toner. Such deteriorating effects reveal themselves in progressive loss of image quality with time in use and may ultimately require the replacement of the total developer package.
In order to alleviate these deteriorating effects, a variety of improvements have been made. For example, the selection of resinous materials and/or adhesion between the surface of the magnetic materials and the coating resins have been examined so as to improve mechanical strength, to thereby reduce cracks, fracture and abrasion of carrier coatings.
Among numerous proposals made regarding resinous materials, resins of crosslinking type have been proposed that are particularly capable of increasing the mechanical strength. In general, these resins include, but are not limited to, acrylic resins, polyester resins and silicone resins, used in combination with a variety of cross linking agents and appropriate additives.
Illustrative examples of the proposed resins and methods include one using crosslinking polycarbodiimide resins discussed in Japanese Laid-Open Patent Application No. 5-127432, a method of crosslinking acrylic resins having specific properties and structure, discussed in Japanese Laid-Open Patent Applications Nos. 5-216282 and 5-216283; a method of forming a composite crosslinking structure consisting of urethane and urea bonds, discussed in Japanese Laid-Open Patent Application No. 5-197211; a method using a silicone resin having specified silane coupling agents, discussed in Japanese Laid-Open Patent Application No. 7-114221; and a method of crosslinking a alcohol hydroxy group containing resin with a phenolic hydroxy group containing resin, discussed in Japanese Laid-Open Patent Application No. 8-87137.
A further method is also proposed for polymerizing resinous materials directly onto the surface of magnetic materials. This is exemplified by a method of interfacially polymerizing and subsequently cross-linking resinous materials coated on the surface of carrier core materials, discussed in Japanese Laid-Open Patent Application No. 6-194881.
The resultant coated materials formed by these methods, however, have drawbacks such as difficulties in separating resinous materials from the core, since their mechanical strength and stability against thermal stress are increased by these methods.
Furthermore, a method is proposed for coating various resinous materials on the surface of magnetic materials to prevent spent toner particles. For example, in a method discussed in Japanese Laid-Open Patent Application No. 62-61948, the hardness of coated silicone resin is said to be increased.
As described hereinabove, many carriers for use in two-component dry developers are formed with cross-linked resinous materials as the coating resin so as to increase mechanical strength and thus to reduce spent toners. As a result, a strong bond is generally formed between the resinous materials and core materials.
The aforementioned degraded developers have been collected to be subsequently discarded. Along with the recent increase in industrial waste and concomitant environmental destruction, recycling of the developers is one of the problems awaiting solution.
As for recovering these developers, two methods have been proposed, one is to remove spent toner from the carrier surface so as to restore developer characteristics, and the other is to remove resinous materials previously coated on carrier to thereby recover core materials for recycled use.
The former method is exemplified by Japanese Laid-Open Patent Application No. 6-149132, in which spent toner particles compressed onto the carrier surface are removed by either heating or cleansing with solvents so as to recycle core materials. In this method, previously coated resin materials are retained and used as a portion of recycled toner. According to this method, therefore, toners themselves which are once spent or degraded, may be recovered for recycled use.
However, the degradation in the above-noted developer characteristics are often caused to some extent not only by spent toners but also by cracking, fracture and abrasion of carrier coatings, to a certain extent. In such a case, carrier properties can not be restored by removing spent toners alone for cycled use. In addition, there are some spent toners which are difficult to remove by the above method. Therefore, further methods are awaited which are more effective for removing the toners. Furthermore, since solvents are used during cleansing processes in the above method and these solvents may necessitate after treatments, methods are again awaited which are more benign to the environment.
The other method is exemplified by Japanese Laid-Open Patent Application No. 47-12286, in which resinous materials previously coated on carrier are removed so as to recover core materials for recycled use. In this process, collected developers are recycled after heating at a relatively high temperature (1000° F.). When this method is applied to carriers coated with thermoplastic resins such as, for example, acrylic resin, even coated resin material can be removed. Therefore, even developers previously degraded not only by spent toners but also by cracking, fracture and abrasion of the coating, can be recoated to be used as core materials for forming recycled carriers.
However, when the above method is applied to a carrier which contains ferrite materials as its core, comprising metal suboxides with inherent magnetic properties, there are disadvantages such as difficulties in restoring the characteristics of these carriers. In addition, it is desirable this method be carried out in a manner that also recycles the heat generated during processing, to thereby reduce undesirable environmental effects. However, since inflammable materials are among the carrier constituents such as, for example, combustion heat generating resins, efficient thermal recycling may not be achieved during the carrier recovery processes.
In addition, when this method is applied to a carrier system which contains thermosetting resin as its coating, a disadvantage is that the thermosetting resin cannot be sufficiently removed from the core.
Furthermore, it has been found that when some of the remainder of core coating resin and/or byproducts by the processing remain adhered, a recycled carrier formed using the above core material has less desirable characteristics compared with a carrier formed using a virgin core material.
That is, the developer characteristics of a developer using such recycled core material are clearly inferior to those of a developer using virgin core material. The difference in characteristics is less when the previously coated resin is removed more thoroughly. Therefore, in order for the developer characteristics of these two developers to be comparable, it is desirable that the residual core coating resin be less, or that the removal rate of the coating resin be greater.
In two-component developers, therefore, the known methods utilized for separating the carrier coating materials for recycling as carriers are not satisfactory in practice, since these methods are not capable of removing the resin materials in a manner benign to the environment and, in addition, may give rise to degrading effects on core properties.
In other words, the conditions in the previously known methods do not meet simultaneously the goals of both removing the resinous material which is tightly bonded chemically and mechanically to the core and retaining desirable properties of magnetic materials used in the core.
None of methods has previously disclosed has focused on the recovery of the magnetic materials of magnetic particles. In particular, this is the case for magnetic material comprising metal suboxide particles having a specific structure and resinous materials, so as not to induce either oxidation or reduction reaction, still retaining crystalline structure thereof and preventing the degradation of their inherent magnetic properties.
That is, since magnetic materials for use in forming core materials are generally composed of substances which are oxidized with relative ease and which have a specific crystalline structure, it is desirable to obviate any chemical change in, for example, oxidation state and/or crystalline structure during process steps.
In this respect, Japanese Laid-Open Patent Application No. 5-53000 discusses the decomposition of resinous materials in water under super- or sub-critical conditions. It is shown that a plurality of resinous materials can be decomposed through hydrolysis and/or pyrolysis to result in their monomer components.
In Japanese Laid-Open Patent Application No. 10-24274, a method is also discussed of decomposing especially thermosetting resins in water under super- or sub-critical conditions. Further, a method is discussed of processing especially chlorine containing wastes in Japanese Laid-Open Patent Application No. 9-111249.
These documents primarily relate to a relatively large amount of resinous wastes and propose several methods for monomerizing the wastes and rendering them harmless, and utilizing the resultant materials as raw materials. The documents also describe appropriate conditions for processing respective resin materials.
Although a plurality of resinous materials are found to be decomposed under super- or sub-critical conditions, as described above, not all practical resinous materials can be decomposed.
A research report “Advanced Research Project for utilizing supercritical liquid compositions”, issued in 1997 by NEDO (New Energy Development Organization), Japan, discusses results of decomposition of several thermosetting resins. As an example for the thermosetting resins, phenol resin is reported to have a low decomposition rate after processed in a supercritical water composition, which may be indicative of charring of the resin. This report also gives several ranges of appropriate processing conditions that can be applied to respective resinous materials.
Further, in Japanese Laid-Open Patent Applications Nos. 10-80674 and 10-87872, methods in general and details of processing steps are discussed, especially with respect to composite materials comprising fiber reinforced plastics and other selected material used as structural materials for ship building, for example.
These documents relate to treatment processes and processing conditions, as described above, for rather specific materials in respective embodiments of the structure and use of the materials. Although they are primarily concerned with the separation of core materials from resin or fibers, no description could be found of recycling the core materials and the change in the material properties. In particular, no disclosure could be found of methods for recovering magnetic particles from particulate magnetic materials composed of metal suboxide particles having a specific structure and resinous materials, without inducing either oxidation or reduction reaction and still retaining crystalline structure thereof, to thereby prevent the degradation of inherent magnetic characteristics.
In addition, core materials in electrophotographic carriers include magnetic particles formed in a highly designed manner such that their particle size is approximately the same within a predetermined range and the shape is spherical as much as possible. In the above documents, no description could be found regarding the effects on the shape and size of the magnetic particles, which may be caused under super- or sub-critical conditions.
As to an apparatus utilizing super-critical water compositions, a plurality of improvements have been discussed for use in processing wastes. As an example, a flow-through type apparatus using super-critical water compositions is discussed in Japanese Laid-Open Patent Application No. 5-31000. In Japanese Laid-Open Patent Application No. 9-77905, another method is discussed, in which useful materials are recovered thorough feeding wastes with water into a screw type extruder used as a reaction vessel. In Japanese Laid-Open Patent Application No. 3-500264, another method is discussed, in which solid products are recovered after process steps using a plurality of reaction vessels provided in series.
According to these documents, the apparatuses are designed to decompose almost all materials fed there into, then transfer resultant materials with water toward downstream throughout process steps. However, when the method is applied to processing such materials as electrophotographic carriers presently contemplated, other consideration should be included. In such a system, magnetic materials are included as the major ingredient in the materials system being processed, and should remain non-decomposed, with their particle size and properties relatively intact throughout the process steps.
The above documents do not teach satisfactory means of solving problems associated with the above system of, for example, carrier materials in regard to methods of utilizing heat, adhesion of reactant residues onto a reaction vessel, and transfer the materials being processed inside the reaction vessels.
As to the super-critical water processing, there are discussions regarding, for example, processing optical fibers in Japanese Laid-Open Patent Application No. 7-306321, and fiber reinforced plastics in Japanese Laid-Open Patent Application No. 10-87872. In these documents, either oxidation or reduction reaction is induced to some extent and that gives rise to a relatively large amount of fiber residues. However, no description could be found on processing the residues.
As described earlier, the method in the present disclosure is applied to processing a magnetic materials system different from the above optical fiber processing in both shape and material properties, that will give rise to different characteristic problems to be solved. That is, since the present magnetic materials generally comprise substances oxidized with relative ease, and having a specific crystalline structure, it is preferable to prevent changes in the oxidation state and/or in crystalline structure, for example, during recycling process steps.
Although supercritical water compositions are quite effective for materials processing as described above, appropriate adjustment of process conditions is important in order to enhance the effect from the economical point of view, among others. When a relatively large amount of water is used as compared with the materials being processed, costs of heat energy may considerably influence the total costs of the processing. However, a certain amount of water can be still necessary to adequately achieve required changes in the materials being processed. That is, the amount of water would need to sufficient for satisfactorily removing coated resins from electrophotographic carriers.
Therefore, as the amount of water is increased for adequately processing the unit weight of materials being processed, resins is removed more thoroughly. Since this, of course, increases processing costs, it is desirable to find conditions to meet both performance and costs of the removing processes.
According to the forgoing, therefore, it is desirable to provide a method for two-components electrostatic image developers for use in electrophotography, capable of separating a tightly bonded resinous material from a core material. This method is preferably carried out without affecting inherent magnetic characteristics to subsequently recycle the core as carriers by re-coating resinous materials, still retaining desirable materials properties. Namely, such an improved method is desirable, being capable of thoroughly removing a resin material from a core material in a manner benign to the environment and alleviating possible degrading effects on core material properties to thereby recycle the core material.
In addition, it is also desirable to provide an apparatus capable of separating a resinous material from a core magnetic material, alleviating the shortcomings described herein above. Namely, a method is desirable which is capable of thoroughly separating a resin material in a manner economical and also benign to the environment, still alleviating possible degrading effects on core material properties to thereby recycle the core material. For materials system such as an electrophotographic carrier, in particular, which generally includes a relatively large amount of materials being processed, an improved apparatus is desirable which is capable of thoroughly separating a coated material through secure material handling in a reaction vessel with good overall heat energy efficiency.